1. Field of Invention
The invention relates to a printing system and method and, more particularly, to a printing system and method allowing a low-resolution printer to perform printing based on print data prepared at high resolution.
2. Description of Related Art
Recently, printers have become increasingly higher in resolution, and laser printers capable of printing at a resolution as high as 1200xc3x971200 dpi have become commercially available. In order to increase the resolution of a printer, it is required to increase a kind of response speed of the printer, for example, by adopting a photoconductive member responsive to a laser beam even when its irradiation time is short, by increasing the modulation frequency of the laser beam, or by speeding print data transmission to a laser beam drive circuit. Further, it is required to increase mechanical accuracy, for example, by increasing rotation accuracy of a laser scanner, which is crucial to formation of a latent image on a photoconductive member based on image data, by increasing rotation accuracy of the photoconductive member, or by increasing image development and transfer accuracy, which is crucial to development of a latent image with toner and transfer of a toner image to recording paper. Especially, when the circumference of the photoconductive member is less than the length of one page of printing paper, formation of a latent image, development of the latent image, and transfer of a developed image concurrently occur on the same photoconductive member. As a result, paper feed accuracy at the image transfer portion becomes a determinant of the overall accuracy of the printer.
As described above, since a laser printer attaining a high resolution of, for example, 1200xc3x971200 dpi requires higher response speed and accuracy, such a printer becomes very expensive compared to a laser printer having a resolution of 600xc3x97600 dpi.
The maximum output speed, at which the printer resolution determined by the above-described mechanical accuracy is stably attained, is termed the process speed of the printer. For example, in the printer using a photoconductive member whose circumference is less than the paper length, the process speed is determined by the paper feed speed at the image transfer portion, and thus the paper feed speed is preset such that the printer can attain a specified resolution.
A direction along which a laser beam is scanned is termed herein a scanning direction, while a direction perpendicular to the scanning direction is termed a sub-scanning direction. The process speed is a speed pertinent to the sub-scanning direction.
Aiming at an increase in resolution, the response speed can be increased to some extent by making the process speed lower than its preset speed. Thus, the response speed will be excluded from the major factors limiting the resolution. However, in this case, the printing speed will be reduced instead. In addition, even when the process speed is reduced, limited mechanical accuracy, such as limited paper feed accuracy, is hard to resolve and directly defines the limitations of the printer. Increasing other mechanical accuracy, for example, by maintaining rotation accuracy of the laser beam scanner high enough to allow its high-speed rotation will result in a price increase. The laser beam scanner, if rotated at high speed, produces noise, and an additional measure is required to reduce the noise, resulting in a further price increase.
Under the above-described circumstances, demands for high-quality printouts at the lowest price are great. Also, there are demands for a laser printer that is even inexpensive and of low-resolution but capable of producing printouts using high-quality image data prepared for a high-resolution laser printer. Such a printer, if available, makes it unnecessary to prepare print data separately for resolutions varying from printer to printer.
In view of the foregoing, a first object of the invention is to provide a printing system and method that allow a low-resolution printer to produce printouts perceived to be comparable to those produced by a high-resolution printer. A second object of the invention is to provide a printing system and method in which printing is selectively performed at a high resolution and a normal resolution. A third object of the invention is to provide a printing system and method in which no displacements are produced in boundaries of a printed image.
To achieve the first and the second objects, a printing system according to one aspect of the invention includes a memory device that stores image data; a first developer that develops print data into first image data having a first resolution in two crosswise directions, the first image data being stored in the memory device; a rearranger that breaks the first image data stored in the memory device into blocks of N consecutive lines, N being not smaller than two, and retrieves therefrom the first image data in blocks of N consecutive lines to rearrange N lines of retrieved image data into one line of image data according to a predetermined rearrangement scheme; a printing device that prints at the second resolution lower than the first resolution; a first printing controller that controls the printing device to execute printing based on the image data rearranged by the rearranger; a second developer that develops print data into second image data having a second resolution in two crosswise directions, the second image data being stored in the memory device; a second printing controller that controls the printing device to execute printing based on the second image data stored in the memory device; and a switching device that switches between the first developer and the second developer prior to development of print data.
In the printing system as described above, the switching device switches between a fine mode and a normal mode when print data is stored in the memory device. In the fine mode, print data is developed into the first image data having the first resolution and stored in the memory device. On the other hand, in the normal mode, print data is developed into the second image data having the second resolution that agrees with the capability of the printing device, and is stored in the memory device.
In the fine mode, the first developer develops print data into the first image data having the first resolution in two crosswise directions. The first image data is stored in the memory device. Then the rearranger breaks the first image data into blocks of N consecutive lines (N being not smaller than two), retrieves the first image data in blocks of N consecutive lines from the memory device, and rearranges the retrieved image data according to a predetermined rearrangement scheme. Finally, the first printing controller controls the printing device to execute printing based on the image data rearranged by the rearranger.
On the other hand, in the normal mode, print data is developed into the second image data having the second resolution in two crosswise directions. The second image data is stored in the memory device. The second printing controller reads the second image data from the memory device and controls the printing device to execute printing based on the read image data, which is not rearranged by the rearranger.
Accordingly, in the fine mode, for example, image data having 2400xc3x971200 dpi is produced based on the image data developed to have a first resolution of 1200xc3x971200 dpi and stored in the memory device. Then, using a printer having a process speed of 600 dpi, such printouts can be produced that appear to be of high resolution and as if produced by a printer having a process speed of 1200 dpi.
On the other hand, on the normal mode, printing can be performed, for example, at a second resolution of 600 dpi.
According to another aspect of the invention, the printing system further includes a mode determiner that determines which mode is designated as a print mode, the fine mode in which printing is executed at the first resolution or the normal mode in which printing is executed at the second resolution. The switching device switches to the first developer when the mode determiner determines that the fine mode is designated, and switches to the second developer when the normal mode is designated.
Accordingly, the print mode can be selectively changed, according to the desired resolution, between the fine mode and the normal mode.
According to another aspect of the invention, the printing system further includes a memory amount determiner that determines whether an amount of memory of the memory device is sufficient to store print data as the first image data. The switching device switches to the first developer when the memory amount determiner determines that the amount of memory is sufficient, and switches to the second developer when the memory amount determiner determines that the amount of memory is insufficient.
With this arrangement, when print data is too large to be stored, as the first image data in the fine mode, in the memory device, the print mode can be changed to the normal mode in which the print data is stored as the second image data having the second resolution. Accordingly, even when the amount of memory is insufficient, printing can be executed at the second resolution that agrees with the printing device""s intrinsic capability.
According to another aspect of the invention, the printing device has the second resolution as a resolution in a sub-scanning direction in which a printing medium is transported and a third resolution, which is higher than the first resolution, as a resolution in a scanning direction perpendicular to the sub-scanning direction.
With this arrangement, in the printing system, printing is executed at the second resolution lower than the first resolution in the sub-scanning direction, and at the third resolution higher than the first resolution in the scanning direction. For example, image data prepared at 1200xc3x971200 dpi is converted into image data with 2400xc3x97600 dpi, and the image data is transmitted to the printing device, such as a laser printer, having a process speed of 600 dpi. Then, image data is outputted in the scanning direction by being converted at a modulation frequency that attains a resolution of 2400 dpi higher than 1200 dpi. As a result, characters and graphics printed on a printing medium appear comparable to those produced by a high-resolution laser printer having 1200xc3x971200 dpi.
According to still another aspect of the invention, the first resolution is N times the second resolution, and the third resolution is N times the first resolution.
With this arrangement, when the first resolution is used as the reference, the second resolution is 1/N times the first resolution and the third resolution is N times the first resolution. For example, provided that N=2 and the first image data is prepared at a first resolution of 1200xc3x971200 dpi, the printing device executes printing at 1/2 times the first resolution in the sub-scanning direction and at 2 times the first resolution in the scanning direction. In other words, the printing device executes printing based on image data rearranged into 2400xc3x97600 dpi. An outputted image is isotropic and distortion-free, that is, it has the same length-to-width ratio as that of the image data prepared to have the first resolution.
According to still another aspect of the invention, the printing device comprises a print engine for a laser printer, and the first printing controller controls the print engine to perform pulse width modulation of a laser beam that is moved in the scanning direction when the printing device executes printing of one line of image data rearranged by the rearranger.
With this arrangement, an excellent gray-scale image can be easily produced.
According to still another aspect of the invention, the rearranger comprises an N-line memory device having a plurality of memory areas for storing N lines of retrieved image data line by line, and a selector that receives the image data on the basis of one bit, line by line, from the plurality of memory areas, rearranges the image data by means of an internal hardware logic circuit, and outputs the rearranged image data.
With this arrangement, the image data can be rearranged more quickly than when rearranged using software.
According to still another aspect of the invention, in accordance with the rearrangement scheme, image data located at same bit positions in respective lines of N lines is repeatedly processed into a bit cell composed of M bits (M being multiples of N) until one line of image data is created, the same bit positions in the respective lines corresponding, in a fixed relationship, to bit positions in the respective bit cells.
With this arrangement, in accordance with the rearrangement scheme, the rearranger repeatedly processes the image data located at same bit positions in respective lines of N lines (bitmapped data in the same column) into a bit cell composed of M bits (M=nN, n being a natural number) until one line of image data is created. The same bit positions in the respective lines correspond, in a fixed relationship, to bit positions in the respective bit cells. More specifically, when N=2, two consecutive lines of image data in the sub-scanning direction are retrieved from the first image data having the first resolution. According to a rearrangement scheme, the two consecutive lines of image data are broken into, for example, 2-bit cells. Then, bit data in the first line and bit data in the second line in each bit cell are rearranged alternately into image data in one-and-the same line. At this time, either the bit data in the first line or the bit data in the second line may be disposed at the first (leftmost) side in the line. According to an alternative rearrangement scheme, when N=2, two consecutive lines of image data in the sub-scanning direction are retrieved, and the two consecutive lines of image data are broken into bit cells, each being composed of 2xc3x972=4 bits. Then, bit data in the first line and bit data in the second line in each bit cell are rearranged alternately into image data in one-and-the same line. Alternatively, when N=3, a bit cell composed of 3xc3x973=9 bits may likewise be used to process image data.
To achieve the first and the third objects of the invention, a printing system according to one aspect of the invention includes a memory device that stores image data; a first developer that develops print data into first image data having a first resolution in two crosswise directions, the first image data being stored in the memory device; a rearranger that breaks the first image data stored in the memory device into blocks of N consecutive lines, N being not smaller than two, and retrieves therefrom the first image data in blocks of N consecutive lines to rearrange N lines of retrieved image data into one line of image data according to a predetermined rearrangement scheme; a printing device that prints at a second resolution lower than the first resolution; and a printing controller that controls the printing device to execute printing based on the image data rearranged by the rearranger. According to the rearrangement scheme, image data located at same bit positions in respective lines of N lines is repeatedly processed into a bit cell composed of M bits (M being multiples of N) until one line of image data is created, and when a bit of image data to be outputted exists at any one of the same bit positions in the respective lines, the bit of image data is disposed in a predetermined bit position in a corresponding bit cell.
In the printing system arranged as described above, in accordance with the rearrangement scheme, the rearranger repeatedly processes the image data located at same bit positions in respective lines of N lines (bitmapped data in the same column) into a bit cell composed of M bits (M=nN, n being a natural number) until one line of image data is created. In addition, when a bit of image data to be outputted (bitmapped data being ON, which indicates a black dot when image data is binary) exists at any one of the same bit positions in the respective lines, the bit of image data is disposed in a predetermined bit position in a corresponding bit cell. More specifically, when N=2, two consecutive lines of image data in the sub-scanning direction are retrieved from the first image data having the first resolution, and the two consecutive lines of image data are broken into bit cells, each being composed of, for example, 2xc3x972=4 bits. For example, when, in a bit cell, bit data in the first line and in the first column, bit data in the first line and in the second column, and bit data in the second line and in the first column are OFF, and bit data in the second line and in the second column is ON, the bit data in the second line and in the second column is disposed at the first (leftmost) position of a new bit cell. In the printing system using such a rearrangement scheme, ON bit data is always disposed on the first (leftmost) side and, as a result, a printed image that has no displacements in boundaries and is perceived to be of high quality is obtained.